Implementing IPv6 over MPLS

Last Updated: August 1, 2012

Multiprotocol Label Switching (MPLS) is deployed by many service providers in their IPv4 networks. Service providers want to introduce IPv6 services to their customers, but changes to their existing IPv4 infrastructure can be expensive and the cost benefit for a small amount of IPv6 traffic does not make economic sense. Several integration scenarios have been developed to leverage an existing IPv4 MPLS infrastructure and add IPv6 services without requiring any changes to the network backbone. This document describes how to implement IPv6 over MPLS.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table at the end of this module.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.

Before the IPv6 Provider Edge Router over MPLS (6PE) feature can be implemented, MPLS must be running over the core IPv4 network. If Cisco routers are used, Cisco Express Forwarding or distributed Cisco Express Forwarding must be enabled for both IPv4 and IPv6 protocols. This module assumes that you are familiar with MPLS.

Information About Implementing IPv6 over MPLS

Benefits of Deploying IPv6 over MPLS Backbones

IPv6 over MPLS backbones enables isolated IPv6 domains to communicate with each other over an MPLS IPv4 core network. This implementation requires only a few backbone infrastructure upgrades and no reconfiguration of core routers because forwarding is based on labels rather than the IP header itself, providing a very cost-effective strategy for the deployment of IPv6.

Additionally, the inherent Virtual Private Network (VPN) and MPLS traffic engineering (MPLS-TE) services available within an MPLS environment allow IPv6 networks to be combined into IPv4 VPNs or extranets over an infrastructure supporting IPv4 VPNs and MPLS-TE.

IPv6 over a Circuit Transport over MPLS

Using any circuit transport for deploying IPv6 over MPLS networks has no impact on the operation or infrastructure of MPLS, and requires no configuration changes to the core or provider edge routers. Communication between the remote IPv6 domains runs native IPv6 protocols over a dedicated link, where the underlying mechanisms are fully transparent to IPv6. The IPv6 traffic is tunneled using the Any Transport over MPLS (MPLS/AToM) or Ethernet over MPLS (EoMPLS) feature with the routers connected through an ATM OC-3 or Ethernet interface, respectively.

The figure below shows the configuration for IPv6 over any circuit transport over MPLS.

Figure 1

IPv6 over a Circuit Transport over MPLS

IPv6 Using Tunnels on the Customer Edge Routers

Using tunnels on the customer edge (CE) routers is the simplest way of deploying IPv6 over MPLS networks with no impact on the operation or infrastructure of MPLS, and no configuration changes to the core or provider edge routers. Communication between the remote IPv6 domains uses standard tunneling mechanisms and requires the CE routers to be configured to run dual IPv4 and IPv6 protocol stacks. The figure below shows the configuration using tunnels on the CE routers.

Limitations on using tunnels involve the manual configuring of a mesh of tunnels on the CE routers, creating scaling issues for large networks.

IPv6 on the Provider Edge Routers

The Cisco implementation of IPv6 provider edge router over MPLS is called 6PE, and it enables IPv6 sites to communicate with each other over an MPLS IPv4 core network using MPLS label switched paths (LSPs). This feature relies on multiprotocol Border Gateway Protocol (BGP) extensions in the IPv4 network configuration on the provider edge (PE) router to exchange IPv6 reachability information in addition to an MPLS label for each IPv6 address prefix to be advertised. Edge routers are configured to be dual stack running both IPv4 and IPv6, and use the IPv4 mapped IPv6 address for IPv6 prefix reachability exchange.

A hierarchy of labels is imposed on the 6PE ingress router to keep the IPv6 traffic transparent to all the core routers. The top label provides connectivity inside the IPv4 MPLS core network and the label is distributed by Label Distribution Protocol (LDP), Tag Distribution Protocol (TDP), or Resource Reservation Protocol (RSVP). TDP and LDP can both be used for label distribution, but RSVP is used only in the context of MPLS-TE label exchange. The bottom label, automatically assigned to the IPv6 prefix of the destination, is distributed by multiprotocol BGP and used at each 6PE egress router for IPv6 forwarding.

In the figure below the 6PE routers are configured as dual stack routers able to route both IPv4 and IPv6 traffic. Each 6PE router is configured to run LDP, TDP, or RSVP (if traffic engineering is configured) to bind the IPv4 labels. The 6PE routers use multiprotocol BGP to exchange reachability information with the other 6PE devices within the MPLS domain, and to distribute aggregate IPv6 labels between them. All 6PE and core routers--P routers in Figure 3--within the MPLS domain share a common IPv4 Interior Gateway Protocol (IGP) such as Open Shortest Path First (OSPF) or Integrated Intermediate System-to-Intermediate System (IS-IS).

Figure 3

6PE Router Topology

The interfaces on the 6PE routers connecting to the CE router can be configured to forward IPv6 traffic, IPv4 traffic, or both types of traffic depending on the customer requirements. 6PE routers advertise IPv6 reachability information learned from their 6PE peers over the MPLS cloud. Service providers can delegate an IPv6 prefix from their registered IPv6 prefixes over the 6PE infrastructure; otherwise, there is no impact on the CE router.

The P routers in the core of the network are not aware that they are switching IPv6 packets. Core routers are configured to support MPLS and the same IPv4 IGP as the PE routers to establish internal reachability inside the MPLS cloud. Core routers also use LDP, TDP, or RSVP for binding IPv4 labels. Implementing the Cisco 6PE feature does not have any impact on the MPLS core devices.

Within the MPLS network, IPv6 traffic is forwarded using label switching, making the IPv6 traffic transparent to the core of the MPLS network. No IPv6 over IPv4 tunnels or Layer 2 encapsulation methods are required.

6PE Multipath

Internal and external BGP multipath for IPv6 allows the IPv6 device to load balance between several paths (for example, the same neighboring autonomous system or subautonomous system, or the same metric) to reach its destination. The 6PE multipath feature uses MP-iBGP to distribute IPv6 routes over the MPLS IPv4 core network and to attach an MPLS label to each route.

When MP-iBGP multipath is enabled on the 6PE device, all labeled paths are installed in the forwarding table with MPLS information (label stack) when MPLS information is available. This functionality enables 6PE to perform load balancing.

Deploying IPv6 on the Provider Edge Routers (6PE)

Specifying the Source Address Interface on a 6PE Router

Two configuration tasks using the network shown in the figure below are required at the 6PE1 router to enable the 6PE feature.

The customer edge router--CE1 in the figure below--is configured to forward its IPv6 traffic to the 6PE1 router. The P1 router in the core of the network is assumed to be running MPLS, a label distribution protocol, an IPv4 IGP, and Cisco Express Forwarding or distributed Cisco Express Forwarding, and does not require any new configuration to enable the 6PE feature.

Figure 4

6PE Configuration Example

Before You Begin

The 6PE routers--the 6PE1 and 6PE2 routers in the figure below--must be members of the core IPv4 network. The 6PE router interfaces attached to the core network must be running MPLS, the same label distribution protocol, and the same IPv4 IGP, as in the core network.

The 6PE routers must also be configured to be dual stack to run both IPv4 and IPv6.

Disables the IPv4 unicast address family for the BGP routing process specified in the previous step.

Note

Routing information for the IPv4 unicast address family is advertised by default for each BGP routing session configured with the neighborremote-as command unless you configure the nobgpdefaultipv4-unicastcommand before configuring the neighborremote-as command.

Specifies the interface whose IPv4 address is to be used as the source address for the peering.

In the context of this task, the interface must have an IPv4 address with a 32-bit mask configured. Use of a loopback interface is recommended. This address is used to determine the IPv6 next hop by the peer 6PE.

Step 7

address-familyipv6[unicast]

Example:

Router(config-router)# address-family ipv6

Specifies the IPv6 address family and enters address family configuration mode.

The unicast keyword specifies the IPv6 unicast address family. By default, the router is placed in configuration mode for the IPv6 unicast address family if the unicast keyword is not specified with the address-familyipv6 command.

Step 8

neighbor{ip-address | peer-group-name| ipv6-address} activate

Example:

Router(config-router-af)# neighbor 192.168.99.70 activate

Enables the neighbor to exchange prefixes for the IPv6 address family with the local router.

Step 9

neighbor{ip-address | ipv6-address}send-label

Example:

Router(config-router-af)# neighbor 192.168.99.70 send-label

Advertises the capability of the router to send MPLS labels with BGP routes.

In IPv6 address family configuration mode this command enables binding and advertisement of aggregate labels when advertising IPv6 prefixes in BGP.

Configuring iBGP Multipath Load Sharing

Perform this task to configure iBGP multipath load sharing and control the maximum number of parallel iBGP routes that can be installed in a routing table.

SUMMARY STEPS

1.enable

2.configureterminal

3.routerbgpas-number

4.maximum-pathsibgpnumber-of-paths

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2

configureterminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3

routerbgpas-number

Example:

Router(config)# router bgp 65000

Enters router configuration mode for the specified routing process.

Step 4

maximum-pathsibgpnumber-of-paths

Example:

Router(config-router)# maximum-paths ibgp 3

Controls the maximum number of parallel iBGP routes that can be installed in a routing table.

Sample Output from the show mpls forwarding-table Command

This example shows output information linking the MPLS label with prefixes using the showmplsforwarding-tablecommand. If the 6PE feature is configured, the labels are aggregated because there are several prefixes for one local label, and the prefix column contains "IPv6" instead of a target prefix.

Sample Output from the show ipv6 route Command

This example shows output information from the IPv6 routing table using the showipv6routecommand. The output shows the IPv6 MPLS virtual interface as the output interface of IPv6 routes forwarded across the MPLS cloud. In this example using the routers in the figure above, the output is from the 6PE1 router.

The 6PE2 router has advertised the IPv6 prefix of 2001:DB8:dddd::/48 configured for the CE2 router and the next-hop address is the IPv4-compatible IPv6 address ::ffff:192.168.99.70, where 192.168.99.70 is the IPv4 address of the 6PE2 router.

Example: Customer Edge Router

This example shows that the serial interface 0/0 of the customer edge router--CE1 in the figure above--is connected to the service provider and is assigned an IPv6 address. IPv6 is enabled and a default static route is installed using the IPv6 address of serial interface 0/0 of the 6PE1 router.

Example: Provider Edge Router

The 6PE router--Router 6PE1 in the figure above--is configured for both IPv4 and IPv6 traffic. Ethernet interface 0/0 is configured with an IPv4 address and is connected to a router in the core of the network--router P1 in the figure above. Integrated IS-IS and TDP configurations on this router are similar to the P1 router.

Router 6PE1 exchanges IPv6 routing information with another 6PE router--Router 6PE2 in the figure above-- using internal BGP (iBGP) established over an IPv4 connection so that all the neighbor commands use the IPv4 address of the 6PE2 router. All the BGP peers are within autonomous system 65000, so synchronization with IGP is turned off for IPv4. In IPv6 address family configuration mode, synchronization is disabled by default.

IPv6 and Cisco Express Forwarding for IPv6 are enabled, the 6PE2 neighbor is activated, and aggregate label binding and advertisement is enabled for IPv6 prefixes using the neighborsend-label command. Connected and static IPV6 routes are redistributed using BGP. If IPv6 packets are generated in the local router, the IPv6 address for MPLS processing will be the address of loopback interface 0.

This example shows that the serial interface 0/0 connects to the customer and the IPv6 prefix delegated to the customer is 2001:DB8:ffff::/48, which is determined from the service provider IPv6 prefix. A static route is configured to route IPv6 packets between the 6PE route and the CE router.

Example: Core Router

This example shows that the router in the core of the network--Router P in the figure above--is running MPLS, IS-IS, and IPv4 only. The Ethernet interfaces are configured with IPv4 address and are connected to the 6PE routers. IS-IS is the IGP for this network and the P1 and 6PE routers are in the same IS-IS area 49.0001. TDP and tag switching are enabled on both the Ethernet interfaces. Cisco Express Forwarding is enabled in global configuration mode.

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Feature Information for Implementing IPv6 over MPLS

The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.

Table 1

Feature Information for Implementing IPv6 over MPLS

Feature Name

Releases

Feature Information

IPv6 over a Circuit Transport over MPLS

12.0(22)S 12.2(14)S 12.2(28)SB 12.2(15)T 12.3 12.3(2)T 12.4 12.4(2)T

In this feature, communication between the remote IPv6 domains runs native IPv6 protocols over a dedicated link, where the underlying mechanisms are fully transparent to IPv6.

IPv6 Using tunnels Over the Customer Edge Routers

12.0(22)S 12.2(14)S 12.2(28)SB 12.2(15)T 12.3 12.3(2)T 12.4 12.4(2)T

Using tunnels on the CE routers is the simplest way of deploying IPv6 over MPLS networks with no impact on the operation or infrastructure of MPLS.

The Cisco implementation of IPv6 provider edge router over MPLS enables IPv6 sites to communicate with each other over an MPLS IPv4 core network using MPLS LSPs.

6PE Multipath

12.2(25)S 12.2(28)SB 12.2(33)SRA 12.4(6)T

The 6PE multipath feature uses multiprotocol internal BGP (MP-iBGP) to distribute IPv6 routes over the MPLS IPv4 core network and to attach an MPLS label to each route.

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Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.